A joint within the human body forms a juncture between two or more bones or other skeletal parts. The ankle, hip, knee, shoulder, elbow and wrist are just a few examples of the multitude of joints found within the body. As should be apparent from the above list of examples of joints, many of the joints permit relative motion between the bones. For example, the ankle permits a hinge movement, the knee allows for a combination of gliding and hinge movements and the shoulder and hip permit movement through a ball and socket arrangement.
The joints in the body are stressed or can be damaged in a variety of ways. Gradual wear and tear is imposed on the joints through the continuous use of a joint over the years. The joints that permit motion have cartilage positioned between the bones providing lubrication to the motion and also absorbing some of the forces direct for the joint. Over time, the normal use of a joint may wear down the cartilage and bring the moving bones in a direct contact with each other. In contrast, in normal use, a trauma to a joint, such as the delivery of a large force from an automobile accident for example, may cause considerable damage to the bones, the cartilage or to other connective tissue such as tendons or ligaments.
Arthropathy, a term referring to a disease of the joint, is another way in which a joint may become damaged. One form of joint disease is arthritis, which is generally referred to a disease or inflammation of a joint that results in pain, swelling, stiffness, instability, and often deformity.
There are many different forms of arthritis, with osteoarthritis being the most common and resulting from the wear and tear of a cartilage within a joint. Another type of arthropathy is osteonecrosis, which is caused by the death of a part of the bone due to loss of blood supply and subsequent degeneration of the cartilage. Other types of arthritis are caused by trauma to the joint while others, such as rheumatoid arthritis, Lupus, and psoriatic arthritis destroy cartilage and are associated with the inflammation of the joint lining.
The hip joint is one of the joints that is commonly afflicted. The hip joint is a ball and socket joint that joins the femur or thighbone with the pelvis. The pelvis has a hemispherical socket called the acetabulum for receiving the head of the femur. Both the head of the femur and the acetabulum are coated with cartilage for allowing the femur to articulate within the pelvis. Other joints commonly afflicted include those of the spine, knee, shoulder, elbow, carpals, metacarpals, and phalanges of the hand. One means to address this affliction is arthroplasty which commonly refers to the making of an artificial joint. In severe cases of arthritis or other forms of arthropathy, such as when pain is overwhelming or when a joint has a limited range of mobility, a partial or total replacement of the joint may be justified. The procedure for replacing the joint varies, of course, with the particular joint in question, but in general involves replacing a terminal portion of an afflicted bone with a prosthetic implant and inserting a member with structural support to serve as a substitute for the cartilage.
The prosthetic implant is formed of a rigid material that becomes bonded with the bone and provides strength and rigidity to the joint and a bearing member chosen to allow for lubrication to the joint. Suitable materials for the implant include metals and composite materials such as titanium, cobalt chromium, stainless steel, ceramic and suitable materials for the bearing include polyethylene, metal and ceramics. A cement may also be used to secure the prosthetic implant to the host bone.
Total hip replacement, for example, involves removing the ball shaped head of the femur and inserting a stemmed implant into the center of the bone, which is referred to as the medullary canal of the bone. The stem implant may be cemented into the medullary canal or may have a porous coated surface for allowing the bone to heal directly to the implant. The stemmed implant has a neck and a ball shaped head, which are intended to perform the same functions as the neck and head of a healthy femur. A polyethylene, metal or ceramic liner with a metal shell is inserted into the acetabulum and acts as socket for receiving the head on the stemmed implant.
Current methods of preparing the rigid elements of a joint to receive components as in joint replacement surgery involve extensive surgical exposure. The exposure must be sufficient to permit the introduction of drills, reamers, broaches, and other instruments for cutting or removing cartilage and bone that subsequently is replaced with artificial surfaces. For total hip replacement; the acetabular articular surface and subchondral bone is removed by spherical reamers, the head is removed with an oscillating saw, and the medullary canal is shaped with broaches and the reamers.
One difficulty with total hip replacement is that the invasiveness of the procedure may cause significant blood loss and extensive rehabilitation because muscle and tendons may be released from the proximal femur to mobilize the femur and gain exposure and access to the acetabular fossa.
Conventional total hip arthoplasty is indicated for painful arthritis of the hip. The procedure involves exposing the hip joint through an incision to provide the surgeon full visualization of the hip joint and the acetabular region and to provide access for surgical power instruments. In order to appropriately prepare the bony structures of the hip joint, the major muscles spanning the joint are commonly disturbed to gain adequate exposure of the joint.
The steps of the procedure include removing the femoral head following by reaming and broaching the femoral canal to prepare the bony surface to support a hip stem. The stem is implanted and may be cemented in place or press fit for bony in-growth. The acetabulum is prepared using a hemispherical reamer to remove cartilage down to the bleeding bone. Once the acetabular surface is prepared, the acetabular component is implanted, either by cementing in place or by press fitting a metal shaft shell bony in-growth.
Surgical exposure on an incision in the skin is necessary to accommodate the bulk and geometry of the components as well as the instruments for bone preparation. The surgical exposure, which may be between six and twelve inches in length, may result in extensive trauma to the skin tissue surrounding the hip joint along with the release of muscles that insert into the proximal femur.
The surgical exposure may increases bleeding, pain, andsoft tissue damage. All of these may contribute to a longer hospitalization and rehabilitation before the patient can be discharged. The bony surfaces subject to this type of surgery include but are not limited to the acetabular fossa, femoral canal, and metaphyseal/diaphyseal region of the femur. Prior to placing the final implants into the prepared spaces, a femoral trial, which may be the broach in some systems, is placed in the femur along with a trial femoral neck and head, and an acetabular trial is placed into the acetabulum to facilitate trial range of motion and to evaluate hip stability prior to placement of the final total hip implants.
For patients that require hip replacements, it is desirable to provide surgical methods and instruments that may be used to gain surgical access to the articulating joint surfaces, to appropriately prepare the bony structures, to provide artificial, articular bearing surfaces, and to close the surgical site, all without substantial damage or trauma to associate muscles, ligaments, or tendons. To obtain this goal, a system or method is needed to enable the articulating surfaces of the joint to be appropriately prepared using minimally invasive instruments and procedures.
Typical acetabular reamers are hemispherical in shape and have sharp raised portions such as that of a cheese grater. The reamers cover the majority of the acetabular surface during reaming. This enables the surgeon to adequately prepare or machine the acetabulum to accept an acetabular shell and liner during total hip arthoplasty.
As surgeons have attempted to reduce the overall size of the incision and develop less invasive procedures, access to the femur and acetabulum are reduced. A need therefore has arisen for instruments that may more easily fit into a smaller incision for use in these less invasive total hip arthoplasty procedures.
Attempts have been made to reduce the size of the acetabular reamer by simply removing material from the spherical shape. This approach, however, is not ideal in that the reamer material is somewhat thin and flexible. Simply removing the material from the hemispherical shape can lead to an inaccurate reamed shape as the reamer's surface rotates within the acetabulum.
The present invention is designed to overcome at least one of the aforementioned problems.